Preparation and structural characterization of tetracoordinated tungsten(II) diazadiene complexes

Article abstract of DOI:10.1016/j.jorganchem.2005.12.046

Reduction in situ of WCl₄(MeCN)₂ with zinc in the presence of diazadiene ligands 1b-f is reported and produces a series of diamagnetic complexes (DAD)WCl₂ 2b-f. All complexes were characterized by ¹H, ¹³C NMR and IR spectroscopic data. The crystal structures of complexes 2b and 2e were solved by X-ray diffraction methods.

Full text of DOI:10.1016/j.jorganchem.2005.12.046

Journal of Organometallic Chemistry 691 (2006) 1857–1861
www.elsevier.com/locate/jorganchem
Preparation and structural characterization of
tetracoordinated tungsten(II) diazadiene complexes
a
b
a,
*
Thouraya Turki , Taha Guerfel , Faouzi Bouachir
a
Laboratoire de Chimie de Coordination, Faculte´ des Sciences de Monastir, 5019 Monastir, Tunisia
b
Laboratoire de Chimie du Solide, Faculte´ des Sciences de Monastir, 5019 Monastir, Tunisia
Received 8 July 2005; received in revised form 2 December 2005; accepted 12 December 2005
Available online 13 February 2006
Abstract
Reduction in situ of WCl4(MeCN)2 with zinc in the presence of diazadiene ligands 1b–f is reported and produces a series of diamag-
netic complexes (DAD)WCl2 2b–f. All complexes were characterized by 1H, 13C NMR and IR spectroscopic data. The crystal structures
of complexes 2b and 2e were solved by X-ray diffraction methods.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Tungsten; Chemical reduction; Tungsten(II) diazadiene complexes; a-Diimine; X-ray crystallographic determination
1. Introduction
‘‘green’’ catalysts [16,17], the use of diimine complexes in
this area of research has remained relatively unexplored.
Only few examples of divalent chromium and molybde-
num containing diazadiene ligands are known [18,19].
Herein, we describe the preparation of divalent tungsten
compounds with diazadiene ligand as well as the structure
of W(II) species in the solid-state by X-ray crystallography.
The diazadiene derivatives 1b–f used in this study are
shown in Table 1.
Diazadienes (DAD, 1) exhibit a rich coordination chem-
istry [1]. In fact, they can formally act as 2-, 4-, 6- or 8-elec-
tron donors. Metal coordination of the heterodiene is
possible in different conformations. The most frequent case
is the chelation of two imine nitrogens by one metal.
Late transition metal complexes of 1,4-diaza-1,3-diene
(DAD, 1) ligands have recently received renewed attention,
primarily due to their usefulness as homogenous polymer-
ization catalysts [2]. As a result, the reaction chemistry of
this class of diimine ligand with a variety of transition met-
als has become well established [1,3–8]. Lately, the interest
in early transition metal chemistry has focused on group 6
complexes that contain chelating diazadiene ligands [9–15].
Coordination of these diazadiene ligands to low-valent
Pt(0) and Pd(0) metal centers was shown to stabilize the
imine functionality towards hydrolysis. Despite a growing
interest in the chemistry of water-soluble organometallic
complexes and their potential application as recoverable
2. Results and discussion
The reduction of WCl4(MeCN)2 with zinc in the pres-
ence of diazadiene ligand, using dichloromethane as sol-
vent, resulted in the formation of the tungsten complexes
WCl2(DAD) 2b–f.
The divalent tungsten(II) compounds containing diaz-
adiene ligands have been isolated as green crystals for
2b–c, orange for 2d–e and yellow for 2f in good yields after
recrystallization in a mixture of CH2Cl2/n-hexane. All of
them are readily soluble in polar organic solvents such as
DMSO, DMF, CH3CN but are insoluble in water. They
have been characterized by 1H, 13C NMR and IR spectros-
copy. Single crystals of 2b and 2e suitable for X-ray
*
Corresponding author. Tel.: +216 98 503 997; fax: +216 71 704 329.
E-mail address: bouachirf@yahoo.de (F. Bouachir).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.046

1858
T. Turki et al. / Journal of Organometallic Chemistry 691 (2006) 1857–1861
Table 1
Diazadiene derivatives used
tion. In each case, a single crystal has been grown from a
mixture of CH2Cl2/n-hexane solution at room temperature.
The ORTEP diagrams of 2b and 2e are shown in Figs. 1
and 2, with details of the structure determination including
unit cell data, data collection parameters, as well as refine-
ment information that is summarized in Table 2. Relevant
bond distances and bond angles, for both structures, are
presented in Tables 3 and 4, respectively.
9
13
10
11
8
7
11
9
12
N-R1
Me
N-R1
N-R1
10
7
6
5
6
5
R1-N
Me
R1-N
N-R1
8
DAD :
1b-c
1d-e
1f
The N1–W–N2 angle of 78.57(17)ꢁ and 81.3(6)ꢁ for
compounds 2b and 2e, respectively, reflects a slightly dis-
torted tetrahedral coordination sphere. These angles are
consistent with known literature values for related com-
plexes [21]. The a-diimine plane (N@CAC@N) is essen-
tially planar (torsion angle N1–C19–C20–N2 = ꢀ0.06ꢁ
and N1–C1–C12–N2 = 0.40ꢁ for compounds 2b and 2e,
respectively); a result that is very similar to other plati-
num(II) complexes [22].
Compound
R1
1b
1c
1d
1e
1f
2,4,6-Me3–C6H2
2,6-Me2–C6H3
2,6-iPr2–C6H3
2-Me–C6H4
C6H5
analysis have been obtained from CH2Cl2/n-hexane at
ambient temperature.
Comparison with other diazadiene complexes [18,19] in
the literature indicates that as the steric bulk of the aryl
ortho substituents increases, the N-aryl rings tend to lie
more perpendicular to the a-diimine plane (N@CAC@N).
The N1–C19 (N1–C1), N2–C20 (N2–C12) and C19–C20
(C1–C12) bond distances are equal to 1.25(7), 1.26(7) and
1.51(7) in 2b and 1.22(19), 1.27(2) and 1.59(2) in 2e, respec-
tively, confirming the conjugated diimine nature of this
ligand [11].
There are no significant differences observed in the W–
Cl and W–N bond distances between the two complexes.
The W–Cl bonds are equal to 2.21(19) and 2.27(2) for 2b
and 2.17(7) and 2.17(6) for 2e while for the W–N bonds
we obtained 2.06(4) and 2.03(4) for 2b and 2.09(13) and
2.06(14) for 2e, respectively.
The new complexes exhibit spectroscopic data in agree-
ment with the proposed structures. 13C NMR spectra of
complexes 2b–f at ambient temperature show the presence
of the expected number of carbon atoms. The substituents
on the aryl groups of the diazadiene ligand are all equiva-
lent as indicated for the C2v and C2-symmetric isomer
which is in accord with the proton NMR spectra. The imi-
nic carbon appears at the range between 159 and 173 ppm,
which is slightly shielded in comparison to the free ligands
(4 ppm). This result is similar to those observed with other
complexes (DAD)MCl2 [M = Cr, Mo] [18,19] and
(DAD)M(CO)4 [20].
In the IR spectra of 2b–f (as KBr pellets), the C@N
stretching vibration is observed at 1600–1660 cmꢀ1, i.e.,
shifted by 10–30 cmꢀ1 to lower frequency in comparison
to the free ligands.
3. Conclusion
The analysis of the structure of both complexes, 2b and
2e, has been conducted using single-crystal X-ray diffrac-
A novel synthetic procedure for divalent tungsten(II)
complexes with a-diimine ligands was described. The new
Fig. 1. ORTEP diagram of 2b Æ CH2Cl2. Thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity.

T. Turki et al. / Journal of Organometallic Chemistry 691 (2006) 1857–1861
1859
Fig. 2. ORTEP diagram of 2e. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms have been omitted for the sake of clarity.
complexes (DAD)WCl2 2b–f display a slightly distorted tet-
rahedral coordination geometry around tungsten.
The reactivities of these complexes in polymerisation
reactions are currently under investigation and the result
will be reported in subsequent publications.
methylene chloride/hexane solution at ambient tempera-
ture. Yields ranged from 65% to 80%.
4.1. Synthesis of [2,4,6-(CH3)3–C6H2-
NC(Me)C(Me)NC6H2-2,4,6-(CH3)3] WCl2 (2b)
4. Experimental
Following general procedure, from WCl4(MeCN)2
(0.49 mmol, 0.20 g), [2,4,6-(CH3)3–C6H2NC(Me)C(Me)N-
C6H2-2,4,6-(CH3)3] (1.4 mmol, 0.471 g). Zinc (2.4 mmol,
0.160 g) in 20 ml of methylene chloride was obtained
0.226 g (yield 80%) of 2b as a green solid after crystalliza-
tion from a mixture of n-hexane/CH2Cl2 (9/1). Decomposi-
tion = 346 ꢁC; IR (tC@N = 1647; 1595 cmꢀ1).
All manipulations are carried out under an atmosphere
of dry and oxygen-free argon with standard schlenk tech-
niques. Diethylether was purified by reflux over sodium
benzophenone ketyl and distilled under argon prior to
use. Methylene chloride and n-hexane were purified from
P2O5 and distilled under argon.
The diazadiene ligands: dab (1b–c) [23], Ar–BIAN (1d–
e), Ph–BIC (1f) [24]; WCl4(MeCN)2 [25] were obtained
according to literature procedures.
1H NMR (300 MHz, CD3CN, 25 ꢁC, d [ppm]): d =
2.11–2.15 (m, 18H, o–o0-CH3, CH3AC@N); 2.38 (s, 6H,
para-CH3); 6.87 (s, 4H, Har).
13C NMR (75.5 MHz, CD3CN, 25 ꢁC, d [ppm]):
d = 18.81 (CH3AC@N); 19.33 (ortho, ortho0-CH3); 21.22
(para-CH3); 129.97 (Cortho); 130.29 (Cmeta); 137.08 (Cpara);
141.07 (Cipso); 173.03 (C@N).
All routine NMR experiments were carried out on a
Bruker AM 300 and infrared spectra on a BioRad FTS-
6000 spectrophotometer.
General procedure for the preparation of (DAD)WCl2. In
an inert atmosphere, WCl4(MeCN)2 (1 equiv.) was added
to diazadiene ligand (3 equiv.) in 20 ml of anhydrous
CH2Cl2. Zinc powder was added (5 equiv.) as a reducing
agent. The solution was stirred at room temperature for
two days. The supernatant was separated by filtration,
and the solvent was removed under vacuum until 3 ml.
The product was precipitated by addition of hexane. Pure
compound was isolated as a solid by crystallization from
4.2. Synthesis of [2,6-Me2–C6H3NC(Me)C(Me)NC6H3-
2,6-Me2] WCl2 (2c)
Following general procedure, from WCl4(MeCN)2
(0.46 mmol, 0.190 g), [2,6-Me2–C6H3NC(Me)C(Me)N-
C6H3-2,6-Me2] (1.39 mmol, 0.764 g). Zinc (2.3 mmol,
0.150 g) in 20 ml of methylene chloride was obtained
0.192 g (yield 76%) of 2c as a brown solid after crystalliza-

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T. Turki et al. / Journal of Organometallic Chemistry 691 (2006) 1857–1861
Table 2
Table 4
Summary of crystallographic data and X-ray experimental details for 2b
2b Æ CH2Cl2 2e
23H30Cl4N2W C26H20Cl2N2W
Selected bond angles (ꢁ) for complexes 2b and 2e
Compound 2b
N1–W–N2
N2–W–Cl1
N2–W–Cl2
C20–N2–W
C20–N2–C7
C7–N2–W
C8–C7–N2
C12–C7–N2
N2–C20–C19
78.57(17)
113.01(14)
115.88(14)
115.0(4)
122.5(5)
122.4(3)
119.6(5)
117.1(5)
116.1(5)
Cl1–W–Cl2
N1–W–Cl1
N1–W–Cl2
C19–N1–W
C19–N1–C1
C1–N1–W
C2–C1–N1
C6–C1–N1
N1–C19–C20
117.44(8)
112.86(14)
112.98(14)
115.0(4)
119.7(5)
125.1(4)
117.9(5)
118.3(5)
115.1(5)
Empirical formula
Formula weight
Crystal system
Space group
Z
C
660.14
Monoclinic
P21/b
615.19
Orthorhombic
P212121
4
4
˚
a (A)
12.810(3)
14.552(4)
14.349(3)
90
90.68(3)
90
11.733(3)
12.003(3)
16.332(5)
90
90
90
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
Compound 2e
N1–W–N2
81.3(6)
111.9(5)
111.6(5)
112.6(11)
118.5(13)
128.9(10)
116.3(8)
123.7(8)
116.2(14)
Cl1–W–Cl2
N1–W–Cl1
N1–W–Cl2
C1–N1–W
C1–N1–C13
C13–N1–W
C14–C13–N1
C18–C13–N1
N1–C1–C12
120.5(3)
116.6(5)
108.4(5)
112.6(10)
118.8(15)
126.5(12)
3
˚
V (A)
2674.6(11)
1.639
2300.1(11)
1.777
N2–W–Cl1
N2–W–Cl2
C12–N2–W
C12–N2–C19
C19–N2–W
C20–C19–N2
C24–C19–N2
N2–C12–C1
qcalc (g cmꢀ3
)
Crystal dimensions (mm)
Temperature (K)
0.15 · 0.38 · 0.59 0.18 · 0.25 · 0.29
293(2)
293(2)
˚
Radiation, k (A)
F(000)
Mo, 0.71073
1296
Mo, 0.71073
1192
123 (2)
2h Range (ꢁ)
Limiting indices
1.59–27.47
ꢀ16 6 h 6 16;
ꢀ13 6 k 6 0;
ꢀ2 6 l 6 18
6335
2.11–27.02
ꢀ8 6 h 6 14;
ꢀ1 6 k 6 15;
ꢀ3 6 l 6 20
3930
114.4(17)
117.0(14)
Number of scanned reflections
4.3. Synthesis of [2,6-iPr2–C6H3-acenaphtene] WCl2 (2d)
{Ar–BIAN,Ar = 2,6-iPr2–C6H3}
Number of independent reflections 5249
3446
Number of observed reflections
Number of parameters varied
Absorption correction
3161
272
1136
215
Empirical
(DIFABS)
XCAD4
SHELX-97
6.97, 21.10
1.021
Empirical
(DIFABS)
XCAD4
SHELX-97
8.81, 24.03
1.004
Following general procedure, from WCl4(MeCN)2
(0.42 mmol, 0.172 g), [(2,6-iPr2-acenaphtene)] (1.26 mmol,
0.605 g). Zinc (2.1 mmol, 0.137 g) in 20 ml of methylene
chloride was obtained 0.225 g (yield 73%) of 2d as orange
brown solid after crystallization from a mixture of
n-hexane/CH2Cl2 (9/1). Decomposition = 375 ꢁC; IR
(tC@N = 1635; 1601 cmꢀ1).
Data reductions programs
Programs used
R1 (Fo), wR2ðF 2oÞ (I > 2r(I)) (%)
Goodness-of-fit on F2
1H NMR (300 MHz, CDCl3, 25 ꢁC, d [ppm]): d = 0.79
(d, 12H, CH3-iPr, JHH = 6.6 Hz); 1,30 (d, 12H, CH3-iPr,
JHH = 6,6 Hz); 3.21 (sept, 2H, CH–iPr, J = 6.9 Hz); 6.65
(d, 2H, H7, J = 7.2 Hz); 7.51–7.19 (m, 8H, 6Har + 2H8);
8.08 (d, 2H, H9, J = 8.4 Hz).
Table 3
˚
Selected bond distances (A) for complexes 2b and 2e
Compound 2b
W–N1
W–Cl1
N1–C19
N1–C1
C6–C15
C2–C13
C4–C14
C19–C20
2.066(4)
2.2138(19)
1.255(7)
1.442(6)
1.518(9)
1.519(9)
1.474(9)
1.511(7)
W–N2
W–Cl2
2.038(4)
2.227(2)
1.264(7)
1.434(6)
1.527(9)
1.518(10)
1.517(9)
N2–C20
N2–C7
C12–C18
C8–C16
C10–C17
13C NMR (75.5 MHz, CDCl3, 25 ꢁC,
d [ppm]):
d = 24.91, 24.63 (CH3–iPr); 29.19 (CH–iPr); 125.38 (C7);
126.16 (Cmeta); 127.29 (Cpara); 128.32 (C8); 129.22 (C9);
131.36 (C6); 133.00 (C10); 139.91 (Cortho); 140.82 (C11);
144.83 (Cipso); 165.31 (C@N).
Compound 2e
W–N1
W–Cl1
2.099(13)
2.173(7)
1.227(19)
1.47(2)
1.42(3)
1.59(2)
W–N2
W–Cl2
N2–C12
N2–C19
C20–C26
2.063(14)
2.178(6)
1.27(2)
1.396(16)
1.201(12)
4.4. Synthesis of [o-Me–C6H4-acenaphtene] WCl2 (2e)
{Ar–BIAN, Ar = o-Me–C6H4}
N1–C1
N1–C13
C18–C25
C1–C12
Following general procedure, from WCl4(MeCN)2
(0.49 mmol, 0.202 g), [o-Me-acenaphtene] (1.4 mmol,
0.535 g). Zinc (2.45 mmol, 0.160 g) in 20 ml of methylene
chloride was obtained 0.206 g (yield 68%) of 2e as orange
solid after crystallization from a mixture of n-hexane/
CH2Cl2 (9/1). Decomposition = 336 ꢁC; IR (tC@N = 1669,
1636 cmꢀ1).
tion from a mixture of n-hexane/CH2Cl2 (9/1). Decomposi-
tion = 340 ꢁC; IR (tC@N = 1644; 1602 cmꢀ1).
1H NMR (300 MHz, DMSO-d6, 25 ꢁC, d [ppm]):
d = 1.76 (m, 18H, o,o0-CH3, CH3AC@N); 6.69–6.89 (m,
6H, Har).
1H NMR (300 MHz, DMSO-d6, 25 ꢁC, d [ppm]):
d = 2.10 (s, 6H, CH3); 6.64 (d,2H, H7, J = 6 Hz); 7.01 (d,
13C NMR (75.5 MHz, DMSO-d6, 25 ꢁC, d [ppm]):
d = 16.31 (CH3AC@N); 18.05 (ortho–ortho0-CH3); 123.75
(Cortho); 124.73 (Cpara); 128.49 (Cmeta); 148.68 (Cipso);
168.29 (C@N).
0
2H, Hmeta, J = 7.5 Hz); 7.25 (d, 2H, Hmeta , J = 7.2 Hz);
0
7.45–7.32 (m, 4H, Hortho;para ); 7.56 (d, 2H, H8); 8.14 (d,
2H, H9, J = 10.5 Hz).

T. Turki et al. / Journal of Organometallic Chemistry 691 (2006) 1857–1861
1861
13C NMR (75.5 MHz, DMSO-d6, 25 ꢁC, d [ppm]):
d = 16.31 (o-CH3); 121.83 (Cortho); 123.52 (C7); 124.56
Copies of this information may be obtained free of charge
from the Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 1223 336 033, or e-mail:
deposit@ccdc.cam.ac.uk).
0
(Cpara); 125.76 (Cortho); 126.16 (Cmeta ); 127.29 (C8); 128.62
(C9); 129.64 (C10); 129.94 (Cmeta); 132.65 (C6); 147.97
(C11); 149.17 (Cipso); 159.03 (C@N).
References
4.5. Synthesis of [Ph–BIC] WCl2 (2f)
[1] (a) G. Van Koten, K. Vrieze, in: F.G.A. Stone, R. West (Eds.),
Advances in Organometallic Chemistry, vol. 21, Academic Press, New
york, 1982, p. 152;
Following general procedure, from WCl4(MeCN)2
(0.39 mmol, 0.16 g), [Ph–BIC] (1.17 mmol, 0.371 g). Zinc
(1.95 mmol, 0.127 g) in 20 ml of methylene chloride was
obtained 0.145 g (yield 65%) of 2f as green solid after crys-
tallization from a mixture of n-hexane/CH2Cl2 (9/1).
Decomposition = 318 ꢁC; IR (tC@N = 1634, 1609 cmꢀ1).
1H NMR (300 MHz, acetone-d6, 25 ꢁC, d [ppm]):
d = 0.69, 0.87, 1.08 (s, 3H chacun, H12,13,14); 1.85–1.95
(m, 4H, H8,9) 3.15 (d, 1H, H10); 6.52–7.27 (m, 10H, Har).
13C NMR (75.5 MHz, acetone-d6, 25 ꢁC, d [ppm]):
d = 11.59, 17.72, 20.45 (C12,13,14); 24.09 (C8,9); 45.28 (C7);
50.66 (C10), 55.28 (C11); 118, 119 (Cortho); 122.73, 124.37
(Cpara); 128.72, 129.29 (Cmeta); 150.07, 151.64 (Cipso);
168.59, 171.36 (C5,6).
(b) G. Van Koten, K. Vrieze, in: G. Wilkinson, R.D. Gillard, J.A.
McCleverty (Eds.), Comprehensive Coordination Chemistry, vol. 2,
Pergamon Press, Oxford, 1987, p. 206;
(c) R. Zoet, G. Van Koten, A.L.J. van der Panne, P. Versloot, K.
VriezeCasper, H. Stam, Inorg. Chim. Acta 149 (1988) 177;
(d) F. Muller, G. Van Koten, K. VriezeDick Herjdenrijk, Inorg.
Chim. Acta 158 (1989) 69.
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[7] J.H. Groen, J.G.P. Delis, W.N.M. Van Leeuwen, K. Vreize,
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X-ray structure determination. Crystals of 2b and 2e suit-
able for X-ray intensity data collection were selected. X-ray
intensity data were collected on a MACH3 Enraf Nonius
diffractometer using monochromated Mo Ka radiation
[8] J.H. Groen, C.J. Elsevier, K. Vreize, W.J.J. Smeets, A.L. Spek,
Organometallics 15 (1996) 3445.
[9] F.W. Grevels, C. Kayron, S. Ozkar, Organometallics 13 (1994) 2937.
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Chim. Acta 300 (2000) 16.
˚
(k = 0.71073 A) at 293 K. Accurate unit cell parameters
[11] F.W. Grevels, K. Kerpen, W.E. Klotzbucher, K. Schaffner, Organo-
metallics 20 (2001) 4775.
and orientation matrix were determined from 25 reflections
in the range 13–15ꢁ for 2b and 12–15ꢁ for 2e. Intensity data
were collected by using the x–2h scan mode with a range of
1.6ꢁ < h < 27.5ꢁ and 2ꢁ < h < 27ꢁ for 2b and 2e, respec-
tively. All the intensity data were corrected for Lorentz
and polarization effects. The crystal structure solution
was carried out with direct methods from the SHELXS-97
permitting the location of all non-Hydrogen atoms. After
anisotropic least-squares refinement, Hydrogen atoms were
placed at their geometrically calculated positions and
refined riding on the corresponding atoms with isotropic
thermal parameters. Final refinement based on the reflec-
tions [I > 2r(I)] converged at R1 = 0.0697, wR2 = 0.2110
and at R1 = 0.0881, wR2 = 0.2403 for 2b and 2e, respec-
tively. The experimental conditions of data collection,
strategy followed for the structure determination, and final
results are given in Table 2.
[12] F. Stoffelbach, R. Poli, P. Richard, J. Organomet. Chem. 663 (2002)
269.
[13] R.S. Herrick, C.J. Ziegler, H. Bohan, M. Corey, M. Eskander, J.
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Supporting information available. Crystallographic data
for the structural analysis of complexes 2b and 2e have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 276433 and 272719, respectively.